Role of biogeochemical parameters in delineating suitable habitats of juvenile Hilsa (Tenualosa ilisha) within an estuary

This investigation characterized the relationship between percentage occurrences of three size classes of Hilsa juveniles (3–5, 5.1–10, and 10.1–15 cm) and six biogeochemical parameters (water temperature, chlorophyll-a, turbidity, salinity, dissolved oxygen, and pH) in the lower part of the tidal riverine to the entire estuarine stretch of Hooghly. These relationships helped us determine the ranges of each biogeochemical parameter for different suitability criteria in three seasons, pre-monsoon (February–May), monsoon (June–September), and post-monsoon (October–January). Salinity had the highest weight (0.37–0.39) followed by chlorophyll-a (0.26–0.30) and turbidity (0.12–0.20). The geospatial data of the biogeochemical parameters were interpolated followed by reclassification with the suitability ranges, separately for each season. These reclassified data were integrated into GIS-based modeling by a multi-criteria decision-making technique (analytical hierarchy process) to generate the habitat suitability maps of juvenile Hilsa. The model-derived information was verified with the indigenous knowledge of the fishers regarding the suitable habitat of juvenile Hilsa by conducting group discussions at 13 locations along the entire study area. The degree of agreement/disagreement between the model and the field information was determined by measuring Kendall’s tau (0.81–0.96) and Kappa coefficients (0.77–0.86), which indicated a strong agreement. In total, 3.80%, 10.12%, and 31.08% of the total river-estuarine area considered for the present study were identified as highly suitable for juvenile Hilsa during pre-monsoon, monsoon, and post-monsoon seasons, respectively. This mapping can act as baseline information for the policymakers for sustainable Hilsa fishing keeping in view the livelihood of fishers.